/// <summary>A byte is read from the SPI interface.</summary>
/// <returns>Received byte from the SPI interface.</returns>
byte SPI_Read               $opc(0x7C)(void);

/// <summary>One byte is sent to the serial interface.</summary>
/// <param name="data">Output byte value.</param>
void SPI_Write              $opc(0x7D)(byte data);

/// <summary>A number of bytes are read from the SPI interface into an array.</summary>
/// <param name="buf">Pointer to byte array.</param>
/// <param name="length">Number if bytes to read.</param>
void SPI_ReadBuf            $opc(0x7E)(byte buf[], byte length);

/// <summary>A number of bytes are sent to the SPI interface.</summary>
/// <param name="buf">Pointer to byte array.</param>
/// <param name="length">Number if bytes to be transferred.</param>
void SPI_WriteBuf           $opc(0x7F)(byte buf[], byte length);

/// <summary>The SPI interface is initialized with the value of ctrl.</summary>
/// <param name="ctrl">Initialization parameter.</param>
void SPI_Enable             $opc(0x80)(byte ctrl);

/// <summary>The SPI will be disabled and the corresponding ports can be used otherwise.</summary>
void SPI_Disable            $opc(0x60)(void);